The invention concerns a device for remoistening a preferably freshly printed, dried paper web by means of spray jets, through which moisturizing agents can be admitted, arrayed above and below the paper web, and spray chambers containing the same.
A device of this kind is known from U.S. Pat. No. 5,813,332 (DE 196 15 198 C1). In this known array, each of the spray chambers is followed immediately downstream by a jet-free condensation chamber, which is equipped with an exhaust air shaft. The flow resistance in this exhaust air shaft is relatively high. On the other hand, the volume of air channelled into the spray chambers is very large. For every liter of moisturizing agent, approximately one cubic meter of compressed air is normally channelled to the spray jets and thus to the spray chambers. There is therefore a danger that the entire volume of air will not be siphoned off through the exhaust air shaft, which exhibits a comparatively high flow resistance, so that there is a risk that part of the air will overcome the air squeegees provided in the area of the inlet or outlet slits of the known array and will not make its way outside. This may lead to the moisturizing agent forming condensation on the outer side of the housing. There is therefore the danger that drops of condensation falling downwards will dirty the paper web. A further disadvantage of the known array can be identified in the fact that the condensation of a remoistening apparatus situated downstream of the chilling roller stand may also make its way to or be formed on the chilling rollers, especially the first chilling roller, which leads to an undesirable swimming effect of the paper web.
Starting from this, it is therefore the task of the present invention to improve a device of the kind mentioned above with simple, cheap means, so that the air channelled to the spray chambers can be relied on to be siphoned off.
According to the invention, this task is achieved in that each spray chamber is arrayed in a dedicated suction chamber, which can be sucked out by means of at least one dedicated extraction fan each.
With these measures, the disadvantages described above of the generic state of the art can be avoided completely. The measures according to the invention guarantee that the air channelled into the spray chambers is captured in the relative dedicated suction chamber and can be relied on to be siphoned off by means of the extraction fan. It is advantageous in this case that there is no danger of any air penetrating outwards, of the related formation of condensation and dirtying of the paper web as a result of falling drops of condensation, nor of the swimming effect of the paper web on the chilling rollers. The advantages that can be achieved with the measures according to the invention are therefore particularly evident in terms of avoiding operational breakdowns and staining and thus of a higher economic yield.
Advantageous embodiments and functional further developments on the above-listed measures are described in the sub-claims. In this way, at least one cooler can be situated upstream of each extraction fan. This cooler functions practically as a condenser, for the purpose of separating out liquids in the form of moisture and oil, which can then be disposed of as the law requires. In this way, the printing room is guaranteed not to be subjected to undesirable oil vapour deposits.
For this purpose, each cooler can be functionally connected to an oil vaporiser arrayed with a dryer provided for the purpose of drying the freshly printed paper web, via a condensation conduit leading preferably through a water separator, so that there is no longer any need to undertake costly disposal of the oil as special refuse.
One further advantageous measure may consist of the fact that the spray and suction chambers can be arrayed in the cooling zone of a dryer provided for the purpose of drying the freshly printed paper web. In this way, the necessary distance between the dryer and a chilling roller stand situated downstream of it is reduced. In addition, this enables the extraction fans simply to blow out into the dryer, which does away with the need for separate exhaust systems and at the same time improves the energy balance of the dryer, as the air blown out by the extraction fans is already pre-heated. A further advantage of these measures can be identified in that not only can the moisture content of the paper web be increased to the desired level in this way, but the paper web can also be subjected to a liquid cooling, which has an advantageous effect in terms of construction volume savings. At the same time, this ensures that the spray streams striking the paper web can be relied on to break down the laminate air layer flanking the paper web, which is laden with solvents, as a consequence of its high penetration force and because of the marked increase in volume ensuing from vaporisation, so that the solvent conveyed together with the air can be relied upon to be sucked out by means of the suction device together with the air siphoned off and cannot penetrate outside.
Additional advantageous embodiments and functional further developments on the above-listed measures are described in the other sub-claims and can be deduced in greater detail from the following description of examples, with the aid of the drawing.